sappirakkosta

Sappirakkosta is a term used in some Finnish-language geology writings to describe rocks that host sapphire crystals within a non-sapphire-dominated matrix. It is not an officially recognized mineral species; rather, it designates a descriptive rock assemblage rather than a mineral name. The term typically applies to metamorphic rocks such as schists or granulites and to pegmatitic intrusions in which corundum (aluminum oxide) occurs as conspicuous crystals. In such rocks, sapphire crystals may range from sub-millimetre to several millimetres in size and can display blue, colorless, or pale hues depending on trace elements like iron and titanium.

Formation is commonly linked to high-temperature metamorphic conditions or late-stage crystallization from aluminous magmas, with fluid histories that concentrate aluminum and silica. The occurrence is rare and fragmentary; sapphiric crystals are of interest to mineralogists and gemstone researchers, but economic mining is generally limited to crystals of suitable size and quality. Because sappirakkosta is a descriptive label rather than a defined mineral, it is primarily used in specific regional literature and within discussions of corundum genesis and metamorphic petrology.

In standard mineral databases, rocks containing sapphire crystals are usually categorized under corundum-bearing rocks or alumina-rich lithologies, rather than under a separate mineral name. The term sappirakkosta remains largely regional to Finnish texts and is not widely adopted in international mineralogical practice. See also: sapphire, corundum, pegmatite, metamorphic rocks, granulite facies.